Implement a Caesar cipher that replaces each letter in the plaintext with a letter a fixed number of positions down the alphabet (A to Z), the position shift number is called "key", which is an integer from 1 to 25. Example: A Caesar cipher with key value 2 encondes plaintext "Hello World" to "Jgnnq Yqtnf".
Step by Step Video Tutorial: https://youtu.be/8OWGVZL_V90 中文视频教程： https://youtu.be/NuWQGKMjxhM
